1. Field of the Invention
This invention relates to a differential unit, particularly suitable for use in motor vehicles as described hereafter, which incorporates a controllable friction assembly for restricting the differential action of the unit.
More particularly, the invention relates to a differential unit comprising:
a housing;
a drivable differential carrier supported in the housing for rotation about an axis;
two output elements rotatable about said axis relative to the differential carrier and connected to respective output shafts;
differential gears rotatably supported by the differential carrier and having driving connection with the output elements to permit differential rotation thereof;
a friction assembly comprising a number of plates rotationally fast with one element of the differential rotatable about said axis, interleaved with a number of plates rotationally fast with another element of the differential rotatable about said axis, and actuating means for axially loading the plates into frictional engagement with one another to restrict said differential rotation of the output elements;
the actuating means comprising an abutment ring fixed relative to the housing, an actuating ring movable axially and angularly relative thereto, and means for causing axial movement of the actuating ring upon said angular movement thereof. Such a differential unit will hereafter be referred to as a differential unit of the kind specified.
2. Description of the Prior Art
A differential unit of the kind specified is disclosed in JP 62-196951A. The cam means operative between the abutment ring and actuating ring comprises opposed circumferentially extending grooves in the rings, with balls engaged in each facing pair of grooves. The depth of the grooves varies linearly as the grooves extend circumferentially. This produces a problem, in that the inclination of the grooves must be limited in order to provide reasonable controllability of the friction assembly, with the result that when the friction plates wear there may not be sufficient axial movement available to the actuating ring to load and operate the friction assembly satisfactorily.